Method and Apparatus for Providing Leak Detection in Data Monitoring and Management Systems

ABSTRACT

Method and apparatus for providing a leak detection circuit for a data monitoring and management system using the guard trace of a glucose sensor by applying a leak detection test signal to determine whether a leakage current is present is provided. The leak detection circuit may include an interface circuit, such as a capacitor, coupled to the guard trace to detect the leakage current when the leak detection test signal is applied to the guard trace, such that the user or patient using the data monitoring and management system, such as glucose monitoring systems, is notified of a failed sensor and prompted to replace the sensor.

RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 11/118,794 filed Apr. 29, 2005 entitled “Method and Apparatusfor Providing Leak Detection in Data Monitoring and Management Systems,”the disclosure of which is incorporated herein by reference for allpurposes.

BACKGROUND

The present invention relates to data monitoring and management systems.More specifically, the present invention relates to method and apparatusfor providing leak detection in sensors used in data monitoring systemssuch as glucose monitoring systems.

Glucose monitoring systems including continuous and discrete monitoringsystems generally include a small, lightweight battery powered andmicroprocessor controlled system which is configured to detect signalsproportional to the corresponding measured glucose levels using anelectrometer, and radio frequency (RF) signals to transmit the collecteddata. One aspect of such glucose monitoring systems include a sensorconfiguration which is, for example, mounted on the skin of a subjectwhose glucose level is to be monitored. The sensor cell may use athree-electrode (work, reference and counter electrodes) configurationdriven by a controlled potential (potentiostat) analog circuit connectedthrough a contact system.

The current level detected by the work electrode of the sensor isrelatively small such that even a small amount of leakage current fromthe reference or counter electrodes typically will affect the signalquality, and thus may have adverse effect upon the accuracy of themeasured glucose level. This is especially true when foreign matter ispresent that causes a false high glucose reading, and which may lead toimproper patient treatment. Furthermore, when the glucose monitoringsystem is calibrated, the offset and gain of the sensor-transmitter pairis established. If the leakage current level changes (i.e., eitherincreases or decreases), then the offset established will likely changeand a resulting gain error may result for future calibration points.

In view of the foregoing, it would be desirable to have an approach todetect leakage current in sensor configuration of data monitoringsystems such as in glucose monitoring systems such that detectivesensors resulting from leakage current may be identified that are notdetecting signals accurately.

SUMMARY OF THE INVENTION

In view of the foregoing, in accordance with the various embodiments ofthe present invention, there is provided a method and apparatus forperforming leak detection in the sensor of a glucose monitoring systemsuch as continuous or discrete glucose monitoring system. The sensor mayinclude subcutaneous or transcutaneous sensor and configured to detectglucose levels of a patient, in particular, diabetic patients.

In one embodiment, there is provided a capacitance to a guard electrodeof the sensor, and a test signal is applied to the guard electrode todetermine whether a current flow can be detected over the capacitance.If the test signal results in the current flow, it is determined thatthe current flow is as a result of the existence of leakage current inthe sensor, and the user or patient is alerted that the sensor is notfunctioning properly. In other words, a detection of the leakage currentprompts the patient that the sensor is no longer measuring accurateglucose levels, and that replacement of the sensor is recommended.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a data monitoring and managementsystem for practicing one embodiment of the present invention;

FIG. 2 is a block diagram of the transmitter of the data monitoring andmanagement system shown in FIG. 1 in accordance with one embodiment ofthe present invention;

FIG. 3 illustrates the front end section of the analog interface of thetransmitter in accordance with one embodiment of the present invention;

FIGS. 4A-4B respectively show detailed illustrations of the current tovoltage circuit and the counter-reference servo circuit of the analoginterface shown in FIG. 3 in accordance with one embodiment of thepresent invention;

FIG. 5 illustrates the leak detection circuit in accordance with oneembodiment of the present invention;

FIGS. 6A-6B illustrate the output response of the current to voltagecircuit in the transmitter of the data monitoring and management systemof FIG. 1 for 100 MOhm leakage resistance between the work and guardelectrodes of the sensor with leak detection test signal held for 500and 250 mseconds, respectively, in accordance with one embodiment of thepresent invention;

FIGS. 7A-7B illustrate the output response of the current to voltagecircuit in the transmitter of the data monitoring and management systemof FIG. 1 for 1,000 MOhm and 10,000 MOhm leakage resistance,respectively, between work and guard electrodes of the sensor, with leakdetection test signal held low for 500 mseconds in accordance with oneembodiment; and

FIG. 8 is a flowchart for performing the leak detection test in thesensor of the data monitoring and management system in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a data monitoring and management system such as, forexample, a glucose monitoring system 100 in accordance with oneembodiment of the present invention. In such embodiment, the glucosemonitoring system 100 includes a sensor 101, a transmitter 102 coupledto the sensor 101, and a receiver 104 which is configured to communicatewith the transmitter 102 via a communication link 103. The receiver 104may be further configured to transmit data to a data processing terminal105 for evaluating the data received by the receiver 104. Only onesensor 101, transmitter 102, communication link 103, receiver 104, anddata processing terminal 105 are shown in the embodiment of the glucosemonitoring system 100 illustrated in FIG. 1. However, it will beappreciated by one of ordinary skill in the art that the glucosemonitoring system 100 may include one or more sensor 101, transmitter102, communication link 103, receiver 104, and data processing terminal105, where each receiver 104 is uniquely synchronized with a respectivetransmitter 102. Moreover, within the scope of the present invention,the glucose monitoring system 100 may be a continuous monitoring system,or a semi-continuous or discrete monitoring system.

In one embodiment of the present invention, the sensor 101 is physicallypositioned on the body of a user whose glucose level is being monitored.The sensor 101 may be configured to continuously sample the glucoselevel of the user and convert the sampled glucose level into acorresponding data signal for transmission by the transmitter 102. Inone embodiment, the transmitter 102 is mounted on the sensor 101 so thatboth devices are positioned on the user's body. The transmitter 102performs data processing such as filtering and encoding on data signals,each of which corresponds to a sampled glucose level of the user, fortransmission to the receiver 104 via the communication link 103.

In one embodiment, the glucose monitoring system 100 is configured as aone-way RF communication path from the transmitter 102 to the receiver104. In such embodiment, the transmitter 102 transmits the sampled datasignals received from the sensor 101 without acknowledgement from thereceiver 104 that the transmitted sampled data signals have beenreceived. For example, the transmitter 102 may be configured to transmitthe encoded sampled data signals at a fixed rate (e.g., at one minuteintervals) after the completion of the initial power on procedure.Likewise, the receiver 104 may be configured to detect such transmittedencoded sampled data signals at predetermined time intervals.Alternatively, the glucose monitoring system 100 may be configured witha bi-directional RF communication between the transmitter 102 and thereceiver 104.

Additionally, in one aspect, the receiver 104 may include two sections.The first section is an analog interface section that is configured tocommunicate with the transmitter 102 via the communication link 103. Inone embodiment, the analog interface section may include an RF receiverand an antenna for receiving and amplifying the data signals from thetransmitter 102, which are thereafter, demodulated with a localoscillator and filtered through a band-pass filter. The second sectionof the receiver 104 is a data processing section which is configured toprocess the data signals received from the transmitter 102 such as byperforming data decoding, error detection and correction, data clockgeneration, and data bit recovery.

In operation, upon completing the power-on procedure, the receiver 104is configured to detect the presence of the transmitter 102 within itsrange based on, for example, the strength of the detected data signalsreceived from the transmitter 102 or a predetermined transmitteridentification information. Upon successful synchronization with thecorresponding transmitter 102, the receiver 104 is configured to beginreceiving from the transmitter 102 data signals corresponding to theuser's detected glucose level. More specifically, the receiver 104 inone embodiment is configured to perform synchronized time hopping withthe corresponding synchronized transmitter 102 via the communicationlink 103 to obtain the user's detected glucose level.

Referring again to FIG. 1, the data processing terminal 105 may includea personal computer, a portable computer such as a laptop or a handhelddevice (e.g., personal digital assistants (PDAs)), and the like, each ofwhich may be configured for data communication with the receiver via awired or a wireless connection. Additionally, the data processingterminal 105 may further be connected to a data network (not shown) forstoring, retrieving and updating data corresponding to the detectedglucose level of the user.

Within the scope of the present invention, the data processing terminal105 may include an infusion device such as an insulin infusion pump,which may be configured to administer insulin to patients, and which isconfigured to communicate with the receiver unit 104 for receiving,among others, the measured glucose level. Alternatively, the receiverunit 104 may be configured to integrate an infusion device therein sothat the receiver unit 104 is configured to administer insulin therapyto patients, for example, for administering and modifying basalprofiles, as well as for determining appropriate boluses foradministration based on, among others, the detected glucose levelsreceived from the transmitter 102.

FIG. 2 is a block diagram of the transmitter of the data monitoring anddetection system shown in FIG. 1 in accordance with one embodiment ofthe present invention. Referring to the Figure, the transmitter 102 inone embodiment includes an analog interface 201 configured tocommunicate with the sensor 101 (FIG. 1), a user input 202, and atemperature detection section 203, each of which is operatively coupledto a transmitter processor 204 such as a central processing unit (CPU).As can be seen from FIG. 2, there are provided four contacts, three ofwhich are electrodes—work electrode (W) 210, guard contact (G) 211,reference electrode (R) 212, and counter electrode (C) 213, eachoperatively coupled to the analog interface 201 of the transmitter 102for connection to the sensor unit 101 (FIG. 1). In one embodiment, eachof the work electrode (W) 210, guard contact (G) 211, referenceelectrode (R) 212, and counter electrode (C) 213 may be made using aconductive material that is either printed or etched, for example, suchas carbon which may be printed, or metal foil (e.g., gold) which may beetched.

Further shown in FIG. 2 are a transmitter serial communication section205 and an RF transmitter 206, each of which is also operatively coupledto the transmitter processor 204. Moreover, a power supply 207 such as abattery is also provided in the transmitter 102 to provide the necessarypower for the transmitter 102. Additionally, as can be seen from theFigure, clock 208 is provided to, among others, supply real timeinformation to the transmitter processor 204.

In one embodiment, a unidirectional input path is established from thesensor 101 (FIG. 1) and/or manufacturing and testing equipment to theanalog interface 201 of the transmitter 102, while a unidirectionaloutput is established from the output of the RF transmitter 206 of thetransmitter 102 for transmission to the receiver 104. In this manner, adata path is shown in FIG. 2 between the aforementioned unidirectionalinput and output via a dedicated link 209 from the analog interface 201to serial communication section 205, thereafter to the processor 204,and then to the RF transmitter 206. As such, in one embodiment, via thedata path described above, the transmitter 102 is configured to transmitto the receiver 104 (FIG. 1), via the communication link 103 (FIG. 1),processed and encoded data signals received from the sensor 101 (FIG.1). Additionally, the unidirectional communication data path between theanalog interface 201 and the RF transmitter 206 discussed above allowsfor the configuration of the transmitter 102 for operation uponcompletion of the manufacturing process as well as for directcommunication for diagnostic and testing purposes.

As discussed above, the transmitter processor 204 is configured totransmit control signals to the various sections of the transmitter 102during the operation of the transmitter 102. In one embodiment, thetransmitter processor 204 also includes a memory (not shown) for storingdata such as the identification information for the transmitter 102, aswell as the data signals received from the sensor 101. The storedinformation may be retrieved and processed for transmission to thereceiver 104 under the control of the transmitter processor 204.Furthermore, the power supply 207 may include a commercially availablebattery.

The transmitter 102 is also configured such that the power supplysection 207 may provide power to the transmitter for a minimum of threemonths of continuous operation after having been stored for 18 months ina low-power (non-operating) mode. In one embodiment, this may beachieved by the transmitter processor 204 operating in low power modesin the non-operating state, for example, drawing no more thanapproximately 1 .mu.A of current. Indeed, in one embodiment, the finalstep during the manufacturing process of the transmitter 102 may placethe transmitter 102 in the lower power, non-operating state (i.e.,post-manufacture sleep mode). In this manner, the shelf life of thetransmitter 102 may be significantly improved.

Referring yet again to FIG. 2, the temperature detection section 203 ofthe transmitter 102 is configured to monitor the temperature of the skinnear the sensor insertion site. The temperature reading is used toadjust the glucose readings obtained from the analog interface 201. TheRF transmitter 206 of the transmitter 102 may be configured foroperation in the frequency band of 315 MHz to 322 MHz, for example, inthe United States. Further, in one embodiment, the RF transmitter 206 isconfigured to modulate the carrier frequency by performing FrequencyShift Keying and Manchester encoding. In one embodiment, the datatransmission rate is 19,200 symbols per second, with a minimumtransmission range for communication with the receiver 104.

Referring yet again to FIG. 2, also shown is a leak detection circuit214 coupled to the guard electrode (G) 211 and the processor 204 in thetransmitter 102 of the data monitoring and management system 100. Asdiscussed in further detail below in conjunction with FIGS. 7-11, theleak detection circuit 214 in accordance with the various embodiments isconfigured to detect leakage current in the sensor 101 to determinewhether the measured sensor data are corrupt or whether the measureddata from the sensor 101 is accurate.

Additional detailed description of the continuous glucose monitoringsystem, its various components including the functional descriptions ofthe transmitter are provided in U.S. Pat. No. 6,175,752 issued Jan. 16,2001 entitled “Analyte Monitoring Device and Methods of Use”, and inU.S. Pat. No. 7,811,231 issued Oct. 12, 2010 entitled “ContinuousGlucose Monitoring System and Methods of Use”, each assigned to theAssignee of the present application, and the disclosures of each ofwhich are incorporated herein by reference for all purposes.

FIG. 3 illustrates the front end section of the analog interface of thetransmitter in accordance with one embodiment of the present invention.Referring to the Figure, the front end section of the analog interface201 includes a current to voltage circuit 301 which is configured tooperatively couple to the work electrode 210 and the guard electrode211, and a counter-reference servo circuit 302 which is configured tooperatively couple to the reference electrode 212 and the counterelectrode 213. It can be further seem from the Figure that the guardelectrode 211 is also coupled to the leak detection circuit 214 of thetransmitter 102. As discussed in further detail below, under theoperation and control of the processor 204 of the transmitter, the leakdetection circuit 214 in one embodiment may be configured to detectleakage current in the sensor 101 of the data monitoring and managementsystem 100.

FIGS. 4A-4B illustrate detailed illustrations of the current to voltagecircuit and the counter-reference servo circuit, respectively, of theanalog interface shown in FIG. 3 in accordance with one embodiment ofthe present invention. Referring to FIG. 4A, the current to voltagecircuit 301 (FIG. 3) in one embodiment includes an operational amplifier402 having a non-inverting input terminal 405, and an inverting inputterminal 404. Also shown in the Figure is a resistor 401 operativelycoupled to the inverting input terminal 404 of the operational amplifier402, and an output terminal 406.

Referring again to FIG. 4A, the work electrode 210 is operativelycoupled to the inverting input terminal 404 of the operational amplifier402, while the guard electrode 211 is operatively coupled to thenon-inverting input terminal 405 of the operational amplifier 402. Itcan be further seen that the work voltage source Vw is provided to thenon-inverting terminal 405 of the operational amplifier 402. In thismanner, in accordance with one embodiment of the present invention, aseparate contact, the guard electrode 211 is operatively coupled to theanalog interface 201 (FIG. 2) of the transmitter 102 (FIG. 2). The guardelectrode 211 as discussed in further detail below is provided at asubstantially equipotential to the work electrode 210 such that anycurrent leakage path to the work electrode 210 (from either thereference electrode 212 or the counter electrode 213, for example) isprotected by the guard electrode 211 by maintaining the guard electrode211 at substantially the same potential as the work electrode 210.

Referring now to FIG. 4B, the counter-reference servo unit 302 inaccordance with one embodiment includes an operational amplifier 407having an inverting input terminal 408 and a non-inverting inputterminal 409, as well as an output terminal 410. In one embodiment, thereference electrode 212 is operatively coupled to the inverting inputterminal 408, while the counter electrode 213 is operatively coupled tothe output terminal 410 of the operational amplifier 407 in thecounter-reference servo unit 302. It can also be seen from FIG. 4B thata reference voltage source Vr is provided to the non-inverting inputterminal 409 of the operational amplifier 407 in the counter-referenceservo unit 302.

Referring back to FIGS. 3 and 4A-4B, in accordance with one embodimentof the present invention, the current to voltage circuit 301 and thecounter-reference servo unit 302 are operatively coupled to theremaining sections of the analog interface 201 of the transmitter 102,and configured to convert the detected glucose level at the sensor unit101 (FIG. 1) into an analog signal for further processing in thetransmitter unit 102. It should also be noted that, in the mannerdescribed, the Poise voltage (for example, at a value of 40 mV) may bedetermined based on the difference between the voltage signal level ofthe work voltage source Vw at the non-inverting input terminal 405 ofthe operational amplifier 402 in the current to voltage circuit 301, andthe voltage signal level of the reference voltage source Vr at thenon-inverting input terminal 409 of the operational amplifier 407 in thecounter-reference servo unit 302.

FIG. 5 illustrates the leak detection circuit in accordance with oneembodiment of the present invention. Referring to the Figure, leakdetection circuit 214 includes, in one embodiment, a resistor 501coupled to the guard electrode 211. As can be seen, the resistor 501 isfurther operatively coupled to a capacitor 503. The capacitor 503 isalso operatively coupled to the processor 204 of the transmitter 102 inthe data monitoring and management system. Referring to FIG. 5, innormal operation, the guard electrode 211 is biased by the guardelectrode bias voltage source is coupled at node or junction 504.

In one embodiment, the guard electrode bias voltage source may be thework voltage source (Vw) shown in FIG. 4A. As can be further seen fromFIG. 5, there is also provided a resistor 502 operatively coupled to thenode or junction 504. In this manner, the guard electrode 211 in thesensor 101 may be configured to function during normal operations toprotect the work electrode 210 from leakage current from the otherelectrodes in the sensor 101, and also, in addition, to receive a leakdetection test signal from the processor 204 at predetermined timeintervals.

The processor 204 in one embodiment may be configured to transmit a leakdetection test signal to the leak detection circuit 214. Morespecifically, when the processor 204 transmits a leak detection testsignal discussed in further detail below, if leakage resistance ispresent in the sensor 101 (for example, due to contamination or waterpresence), a leakage current will flow from the work electrode 210 tothe guard electrode 211 over the resistor 501 and capacitor 503 in theleak detection circuit 214. In turn, due to the current flow from thework electrode 210 to the guard electrode 211, the current to voltagecircuit 301 (FIG. 3) in the transmitter 102 is configured to detect thecurrent flow path, and correspondingly signal the processor 204 thatleakage current exists in the sensor 101. The output response of thecurrent to voltage circuit 301 (FIG. 3) based on the detection ofleakage current described above is shown in FIGS. 6A-6B and 7A-7B asdescribed in further detail below.

On the other hand, if the leakage resistance level is below a nominalthreshold level (and thus not substantially impeding sensor 101function), then substantially no leakage current exists from the workelectrode 210 to the guard electrode 211 that can be detected by thecurrent to voltage circuit 301 in the analog front end of thetransmitter 102.

For example, referring back to FIG. 4A, in one embodiment, the guardelectrode 211 is normally held at the signal level of the work voltagesource Vw which may be within 12 millivolts of the voltage signal levelat the work electrode 210. During normal operation, this helps reduceleakage current affecting the work electrode 210. When it is desired totest for the leakage current in the sensor 101, a leak detection testsignal may be applied to the guard electrode 211 from the processor 204of the transmitter 102 to detect leakage current in the sensor 101 asdiscussed in further detail in conjunction with FIG. 8 below.

In operation, during the leak detection test, the leak detection testsignal (normally held at 3 Volts) from the processor 204 is switchedfrom the three (3) Volts to zero (0) Volts. If moisture or otherconductive contamination is present in the sensor 101, leakage currentwill flow into the capacitor 503 from the guard electrode 211 at a ratethat is a function of the leakage resistance between the work electrode210 and the guard electrode 211. This current produces a correspondingoutput signal from the transimpedance operational amplifier 402 (FIG.4A) which is the current to voltage function that measures the sensor101 current or signal.

Referring to FIGS. 4A, 6A-6B and 7A-7B, the magnitude of the outputsignal from the transimpedance amplifier 402 (FIG. 4A) is a function ofthe time that the leakage test signal is held at the zero (0) Volt, andalso the leakage resistance. This can be seen from the FIGS. 6A-6B and7A-7B discussed in further detail below. Thus, it is possible to detectthe presence of a leakage current in the sensor 101 of the datamonitoring and management system 100, and alert the user that themeasured values received from the sensor 101 may be inaccurate.

Referring back to FIG. 5, the capacitor 503 in one embodiment mayinclude a ceramic capacitor with a very high leakage resistance, forexample, a 10 GOhms of leakage resistance. Furthermore, within the scopeof the present invention, while the capacitor 503 is used in the leakdetection circuit 214 to transfer alternate current (A/C) signals whileblocking direct current (D/C) signals, thereby creating no offset, aninterface circuit may be used such as a resistor, field effecttransistor (FET), an inductor, or any other circuit element which can beconfigured to transfer a signal from the processor 204 to the guardelectrode 211. Moreover, the leak detection test signal within thepresent invention may include a digital signal or an analog signal suchas a sine wave or a pulse which may also be varied in magnitude. Each ofthese analog and digital signals can also be varied in frequency ordriven as a single pulse leak detection test signal.

FIGS. 6A-6B illustrate the output response of the current to voltagecircuit 301 of the transmitter 102 for 100 MOhm leakage resistancebetween the work and guard electrodes with leak detection test signalheld for 500 and 250 mseconds, respectively, in accordance with oneembodiment of the present invention. More specifically, these Figuresillustrate the response to a 100 MOhm leakage resistance that existsbetween the guard electrode 211 and the work electrode 210 of the sensor101, where the response signal shown are the output of thetransimpedance amplifier 402 (FIG. 4A) as detected by the processor 204in the transmitter 102.

By comparing the responses shown in these Figures, the difference inresponse between a 500 millisecond test signal and a 250 millisecondleakage test signal period can be seen. In other words, the length ofthe leak detection testing period is directly correlated with thesensitivity of the leakage detection and thus the accuracy of theleakage detection. That is, the longer the duration of the leakdetection test signal, the higher the resolution of the test signal oraccuracy. In other words, referring to FIGS. 6A-6B, it can be seen thatin FIG. 6A, the duration of the leak detection test signal wasmaintained at 500 milliseconds which yielded a peak signal at greaterthan 300 ADC (analog to digital converter) counts corresponding to thevoltage level, and which in turn, corresponding to the leakage currentin the sensor 101 with the 100 Mega Ohm leakage resistance. On the otherhand, as shown in FIG. 6B, with the duration of the leak detection testsignal at 250 milliseconds, the peak signal was greater than 100 ADCcounts based on the same 100 Mega Ohm leakage resistance.

FIGS. 7A-7B illustrate the output response of the current to voltagecircuit 301 in the transmitter 102 of the system 100 (FIG. 1) for 1,000MOhm and 10,000 MOhm leakage resistance, respectively, between work andguard electrodes, with leak test signal held low for 500 mseconds inaccordance with one embodiment. More specifically, FIGS. 7A and 7Billustrate additional examples of a much lower leakage current with asubstantially higher leakage resistance between the work electrode 210and the guard electrode 211 of the sensor 101. In particular, it can beseen from the Figures that the leak detection test approach as disclosedin accordance with the various embodiments of the present invention issuitable to detect very high values of leakage resistance. For example,referring to FIG. 7A, with leakage resistance of 1000 MOhms and aleakage detection test signal duration of 500 milliseconds, the outputresponse of greater than 15 ADC counts was detected, which can bedetected and identified as the leakage current in the sensor 101. InFIG. 7B, an even higher leakage resistance of 10,000 Mega Ohms was usedat a leakage detection test signal duration of 500 milliseconds whichyielded an output response of approximately 3 ADC counts which can stillbe detected, so as to identify the presence of the leakage current inthe sensor 101.

FIG. 8 is a flowchart for performing the leak detection test in thesensor of the data monitoring and management system in accordance withone embodiment of the present invention. Referring to the Figure, atstep 801, an iterative variable N is set to zero (0) and the leakdetection signal bit is set to Low. In one embodiment, a counter or alatch in the processor 204 may be configured to set the iterativevariable to zero and to store that value (for example, in its internalmemory), and at step 802, the leak detection signal from the processor204 may be set at zero volts. Thereafter at step 803, the signalresponse on the guard electrode 211 is measured. For example, in oneembodiment, the processor 204 is configured to detect a current on theguard electrode 211 in response to the leak detection signal set at Low(0 volts) from the processor 204.

Referring to FIG. 8, at step 804, the processor 204 is configured todetermine whether the detected response at step 803 exceeds a normalsensor level, which, the processor 204 has pre-stored. For example, thenormal sensor level in one embodiment may include the sensor signallevel which was measured just prior to the leak detection test routinediscussed herein. In one embodiment, an additional tolerance may beadded to the sensor signal level measured prior to the leak detectionroutine discussed herein, where the tolerance level corresponds to anacceptable leakage level.

If the response compared at step 804 is not greater than the normalsensor level, then at step 805, it is determined that no leakage currentis detected, and the procedure terminates. Referring back to the Figure,if at step 804 it is determined that the response measured at step 803is not greater than the normal sensor level, then at step 806, theiterative variable is retrieved and compared to determine whether itexceeds a leakage confirmation value. In one embodiment, the leakageconfirmation value may be three. In other words, if three consecutiveresponse measurement detects the response to be greater than the normalthreshold level (step 804), then the leakage in the sensor 101 isconfigured and flagged for the user to replace the sensor 101. Referringback to FIG. 8, if at step 806 it is determined that the iterativevariable N is greater than the leakage confirmation value, then at step807, it is confirmed that a leakage current is detected and the user maybe notified that the data received from the sensor 101 may no longer beaccurate. On the other hand, if at step 806 it is determined that theiterative variable N is not greater than the leakage confirmation value,then at step 808, the leak detection bit is set to High (e.g., 3 Volts),and the routine at step 809 waits for the settling time period. Thesettling time may be based on the selected leak detection signalduration, and in one embodiment, may be in the order of 2 or 3 seconds.Thereafter at step 810, the iterative variable N is incremented by one(1), and the routine returns to step 802.

In an alternate embodiment of the present invention, the routine mayalso include an additional step of measuring the sensor signal level atthe sensor 101 (FIG. 1) after incrementing the iterative variable N 810and prior to returning to the leak detection routine at step 802. Inthis case, the normal sensor level at step 804 to which the measuredresponse (step 803) is compared will be the measured sensor signal levelat the additional step described above.

In the manner described above, an apparatus including a leak detectioncircuit in one embodiment of the present invention includes a guardcontact, an interface circuit coupled to the guard contact, a processorcoupled to the interface circuit, the processor configured to drive aleak detection test signal via the interface circuit to the guardcontact, where the processor is further configured to detect a leakagesignal in response to the leak detection test signal.

The interface circuit may in one embodiment include a capacitor, andfurther, the leak detection test signal may include a digital signal oran analog signal.

Moreover, the guard contact may include in one embodiment the guardelectrode of a sensor.

Furthermore, the sensor may include a plurality of electrodes, one ofthe plurality of electrodes including a work electrode and a guardelectrode, the guard electrode including the guard trace, where theleakage signal detected by the processor includes a sensor signal fromthe sensor.

An apparatus including a leak detection circuit in another embodimentincludes a guard electrode, a capacitor coupled to the guard electrode,and a processor coupled to the capacitor, the processor configured todrive a leak detection test signal via the capacitor to the guardelectrode, where the processor is further configured to detect a leakagesignal in response to the leak detection test signal.

The capacitor in one embodiment may include a ceramic capacitor.

In a further embodiment, the apparatus may also include a sensor, thesensor having a plurality of electrodes, one of the plurality ofelectrodes including a work electrode and the guard electrode, andfurther, where the leakage signal detected by the processor may includea sensor signal from the sensor.

A method of providing a leak detection circuit in a further embodimentof the present invention includes the steps of providing a guardcontact, coupling an interface circuit to the guard contact, driving aleak detection test signal via the interface circuit to the guardcontact, and detecting a leakage signal in response to the leakdetection test signal.

In one aspect, the detecting step may include the step of consecutivelydetecting the leakage signal a predetermined number of iterations, wherein one embodiment, the predetermined number of iterations includesthree.

Further, the step of driving the leak detection test signal may includethe step of setting a leak detection bit to zero.

In the manner described above, in accordance with the variousembodiments of the present invention, there is provided a method andapparatus for performing leak detection in a sensor configuration foruse in data monitoring and management system such as glucose monitoringsystems (continuous or discrete). In particular, in accordance with thepresent invention, it is possible to easily and accurately detectleakage current in the sensor configuration such that the signalintegrity of the measured signals from the sensor can be maintained, andfurther, the user or patient of the data monitoring and managementsystem may be alerted of the leakage detection in the sensor to replacethe same in the system.

Various other modifications and alterations in the structure and methodof operation of this invention will be apparent to those skilled in theart without departing from the scope and spirit of the invention.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments. It isintended that the following claims define the scope of the presentinvention and that structures and methods within the scope of theseclaims and their equivalents be covered thereby.

1. An analyte monitoring apparatus, comprising: a leak detection circuitoperatively coupled to at least one electrode of a transcutaneouslypositioned analyte sensor; and a processor operatively coupled to theleak detection circuit, the processor configured to generate a leakdetection test signal; wherein the leak detection circuit is configuredto detect a leakage current based on the leak detection test signal andto generate a leakage signal upon detection of a leakage current, andfurther wherein the processor is configured to receive the leakagesignal from the leak detection circuit in response to the leak detectiontest signal.
 2. The apparatus of claim 1 further including an interfacecircuit operatively coupled to the processor, the interface circuitconfigured to transfer the leak detection test signal to the at leastone electrode of the analyte sensor.
 3. The apparatus of claim 2 whereinthe processor is configured to drive the leak detection test signal tothe interface circuit.
 4. The apparatus of claim 2 wherein the interfacecircuit includes a capacitor.
 5. The apparatus of claim 1 wherein theprocessor is configured to drive the leak detection test signal to theat least one electrode of the analyte sensor.
 6. The apparatus of claim1 wherein the leak detection test signal includes one of a digitalsignal or an analog signal.
 7. The apparatus of claim 1 wherein theleakage signal received by the processor includes an analyte relatedsignal from the analyte sensor.
 8. The apparatus of claim 1 wherein theprocessor is further configured to determine whether the receivedleakage signal exceeds a predetermined sensor signal level.
 9. Theapparatus of claim 8 wherein the predetermined sensor signal levelincludes a measured sensor signal level, wherein the measured sensorsignal level is measured by the processor at a predetermined timeinterval.
 10. The apparatus of claim 8 wherein the predetermined sensorsignal level includes a tolerance level that corresponds to anacceptable current leakage level.
 11. The apparatus of claim 8 whereinthe processor is further configured to output a notificationcorresponding to the received leakage signal when the received leakagesignal exceeds the predetermined sensor signal level a predeterminednumber of consecutive times.
 12. The apparatus of claim 1 wherein theprocessor is further configured to generate and transmit subsequent leakdetection test signals at predetermined time intervals.
 13. Theapparatus of claim 1 wherein the leak detection circuit comprises aresistor operatively coupled to a capacitor, the capacitor operativelycoupled to the processor.
 14. The apparatus of claim 13 wherein theresistor is operatively coupled to the at least one electrode.
 15. Theapparatus of claim 1 wherein the leak detection circuit has a leakageresistance between 100 MegaOhms and 10,000 MegaOhms.
 16. The apparatusof claim 1 wherein the leak detection test signal has a duration of lessthan one second.
 17. The apparatus of claim 16 wherein the leakdetection test signal has a duration of between 250 milliseconds to 500milliseconds.
 18. A method of providing leak detection, comprising:generating, using a processor, a leak detection test signal; detecting,using a leak detection circuit operatively coupled to at least oneelectrode of an analyte sensor, a leakage current based on the leakdetection test signal; generating, using the leak detection circuit, aleakage signal upon detection of a leakage current; receiving, using theprocessor, the leakage signal from the leak detection circuit inresponse to the leak detection test signal.
 19. The method of claim 18further including transferring, using an interface circuit, the leakdetection test signal to the at least one electrode of the analytesensor.
 20. The method of claim 19 further including driving, using theprocessor, the leak detection test signal to the interface circuit. 21.The method of claim 18 further including driving, using the processor,the leak detection test signal to the at least one electrode of theanalyte sensor.
 22. The method of claim 18 wherein the leak detectiontest signal includes one of a digital signal or an analog signal. 23.The method of claim 18 wherein the leakage signal received by theprocessor includes an analyte related signal from the analyte sensor.24. The method of claim 18 further including determining, using theprocessor, whether the received leakage signal exceeds a predeterminedsensor signal level.
 25. The method of claim 24 wherein thepredetermined sensor signal level includes a measured sensor signallevel, wherein the measured sensor signal level is measured by theprocessor at a predetermined time interval.
 26. The method of claim 24wherein the predetermined sensor signal level includes a tolerance levelthat corresponds to an acceptable current leakage level.
 27. The methodof claim 24 further including outputting, using the processor, anotification corresponding to the received leakage signal when thereceived leakage signal exceeds the predetermined sensor signal level apredetermined number of consecutive times.
 28. The method of claim 18further including generating and transmitting, using the processor,subsequent leak detection test signals at predetermined time intervals.29. The method of claim 18 wherein the leak detection test signal has aduration of less than one second.
 30. The method of claim 29 wherein theleak detection test signal has a duration of between 250 milliseconds to500 milliseconds.